Los Angeles police say that Lonnie Franklin Jr. may be the “grim sleeper” serial killer they have sought for more than 20 years. And if indeed they do have their man, they have his son to thank—for getting arrested himself.

Franklin is one of the first major suspects nabbed by police using familial DNA. With this controversial method, investigators look for partial matches between DNA left at a crime scene and DNA profiles that are stored in police databases; a partial match may indicate that the person is related to the target individual sought by the cops.

The trail began to heat up when the DNA of Franklin’s son was entered in a state database after he was convicted in a weapons case, authorities said. The son’s DNA was similar to genetic material found on the victims, and authorities soon began following around Franklin to get his DNA and see if he was the suspected killer [AP].

The cops posed as waiters at a restaurant where the elder Franklin ate, which is how they obtained a complete DNA sample from him–they grabbed a plate and napkin he tossed after eating a slice of pizza. The investigators say that when they found the match to the samples in their evidence, it eased 25 years of frustration at not being able to track him down.

In 2009, LAPD Det. Dennis Kilcoyne, who led a special unit assigned to find the Grim Sleeper, expressed frustration with knowing who the killer was, but only in a language of numbers and dashes. “We’ve got this beautiful DNA profile — all these dashes and dots, and this and that, but there’s no name to go with it,” Kilcoyne said [CNN].

It was just two years ago that California Attorney General Jerry Brown gave the OK to testing the state’s DNA data bank for these familial matches. Colorado is the only other state that currently allows the practice. Brown promises that only convicted felons are in that database for testing, but that’s just the thing that raised the hackles of opponents.

Familial DNA database searches have come under fire from privacy and civil liberty advocates, who argue, among other things, that they put more minorities, who are disproportionally represented in the database, in an at-risk group [ABC News].

However, as DISCOVER blogger Razib Khan writes at Gene Expression, this testing is coming whether we like it or not (and besides, it’s probably more reliable than eyewitness testimony or fingerprinting). So, Khan says, the issue we should worry about is not privacy but accuracy.